The lead acid battery is widely used in many fields for power storage, such as automobile, telecommunication, railroad, ships, electric vehicles, wind power, solar energy, etc. as a consumptive-material product. It includes a pole plate made up of alloy lead; diachylon consisting of lead sulfate, lead dioxide and lead monoxide; electrolyte containing mainly diluted sulfuric acid; plastic battery enclosure, upper cover and separator, etc. Its annual consumption is huge. If every element of the waste lead acid battery can be substantially recovered for reuse, especially in the production of lead acid batteries so as to implement full cycle regeneration of the waste lead acid battery, the economic benefit is very significant and there is a great social benefit from the associated energy-saving, consumption reducing and environment protection.
However, the known conventional regeneration method of waste lead acid batteries not only wastes a large amount of resource and energy, but also merely recovers parts with high commercial value, such as pole plate and diachylon as well as plastic enclosure from the waste battery. Only simple treatment or even no treatment is made for the other parts of the waste battery, such as plastic separator and electrolyte, and some other parts are simply thrown away without any treatment. Thus, such method is unable to implement full cycle regeneration of the waste lead acid battery, leading to serious problems of environment pollution: the insufficiently treated waste batteries are themselves a serious pollution source and cause the primary pollution; then, the flaws of the regeneration process can cause the secondary pollution. As a result, the waste lead acid battery has become a difficult common environment protection problem for the world.
At present, the conventional regeneration method of waste lead acid batteries includes mainly pyrometallurgical reduction method and electrolysis reduction technology (or wet-treatment method) as detailed below:
Pyrometallurgical Reduction Process
Pyrometallurgical reduction process is a regeneration process to recover diachylon. It has the following shortcomings:
(1) During the pyrometallurgical reduction process, it will cause the secondary pollution due to the reducing agent added which produces a lot of residue. The general pyrometallurgical residue rate of non-converted desulphurization of is 25%˜30%, and the residue rate of converted desulphurization is 10%˜15%. Both type residues are the waste, which cannot be recovered by the system.
(2) During the pyrometallurgical reduction process, it cannot be avoided to produce a lot of high temperature CO2, nitride gas and minim PbO, SO2, dioxin gas to pollute the environment. Although oxygen-enriching, most-environment friendly liquefied gas or natural gas are used as fuel, and the best dust collection unit is selected, it cannot be avoided to cause the problem to pollute air due to PbO and traces of PbSO4 produced during the direct high-temperature reduction process.
(3) The metal recovery rate of the pyrometallurgical reduction process is low. The lead retained in the residue is as high as 1%˜2% for pyrometallurgical process in general. It can reach 3%˜8% in worst scenarios. As the residue contains more metal, resource is wasted and the secondary pollution will be caused.
For both the pyrometallurgical reduction process and electrolytic reduction process, it is often necessary to subject the lead sulfate (PbSO4) of the diachylon in waste batteries to a desulphurization process. At present, there are two commonly-used desulphurization methods, as follows:
(I) Raw Material Mixing High-Temperature Melting Method
At present, in the domestic market, more than 90% of smelting method to recover waste battery is using a direct coal-fired reverberatory furnace. Using this method, it is not necessary to separate metal lead and diachylon from the waste battery plate, and the diachylon is mixed directly with scrap iron, sodium carbonate, reducing coal, etc. to have a substitution reaction under a high-temperature condition. As there is no smashing and separating process for the pole plate of the waster battery, it is not an ideal condition for the diachylon in the pole plate to contact with a lead sulfate state, added in with scrap iron, sodium carbonate, reducing coal, etc. Under a high-temperature condition with direct coal burning (over 1000° C.), the lead sulfate part is separated out to produce sulfur trioxide (SO3) gas. A part of PbSO4 and scrap iron is reduced into metal lead in substitution reaction and produces a lot of iron sulfide residue. As a large quantity of air enters during combustion process, SO3 gas contents are low. It is difficult to be recovered such low concentrations of SO3 to be used in manufacturing sulfuric acid and can only be discharged as a waste. In addition, as there is no special desulphurization neutralization unit, the waste SO3 gas will cause the secondary pollution. This method produces the waste residue at a rate of 25˜30% of the initial material, further causing a serious pollution of solid waste. Furthermore, the production cost is high and resource waste is serious due consumption of a large quantity of scrap iron converted into waste residue.
(II) Smashing Pre-Treatment Substitution Method of Waste Battery at a Normal Temperature
This method is to make a smashing pre-treatment to waste battery to separate metal lead and oxide diachylon. The PbSO4 in diachylon undergoes a substitution reaction at a normal temperature with Na2CO3 or NaOH added in. Its reaction is shown as follows:PbSO4+Na2CO3═PbCO3+Na2SO4 PbSO4+NaOH═PbO+Na2SO4 
The produced PbCO3 and PbO undergo a smelting reduction reaction in the converter. During the smelting process, no SO2 is produced. This method this is substantially free of SO2 pollution. But the method consumes a large quantity of expensive Na2CO3 or NaOH material to produce the low-value Na2SO4, which has little demand on the market. The cost of smelting recovery is high and obtained sodium sulfate cannot be reused in the battery manufacture.
Table 1 is an effect comparison of the above two types of desulphurization processes.
Process methodSmashing pre-treatmentRaw material mixingsubstitution method of waste batteryEffect comparisonhigh-temperature melting methodat a normal temperatureRaw materialNo smashing and separatingSmashing and separating equipment istreatment stateequipmentneeded.Consumable materialScrap iron, sodium carbonate,Sodium carbonate, reducing coalof desulphurizationreducing coalGas produced40-50% PbSO4 is dissociated toSubstitution at a normal temperature toproduce SO3, which is 50 KG/T lead.produce gas. Infinitesimal residualAs a large quantity of air is insufflatedPbSO4 is smelted to produce SO2 gasinto direct combustion, SO3at a high temperature.concentration is low. It is difficult toOxygen-enriched fuel is adopted. Thebe used. It is discharged after simplewaste gas reaches the dischargetreatment and does not reach thestandard after treatment. It is difficultenvironment standard of discharge,to reuse the waste heat.causing serious pollution.Residue producedResidue 300 KG/T lead produced, noResidue 100 KG/T lead produced, novalue in use and is handled asvalue in use and is handled asdangerous waste.dangerous waste.Cycle regenerationOnly recover metal lead, noOnly recover metal lead, to produceeffectby-product produced, to produce a200 KG Na2SO4/T lead, which canlarge quantity of waste gas/residue,only be sold as a by-product and haswhich cannot be reused.little demand on the market. The costis high.
The above two desulphurization processes adopt a substitution reaction principle, to use expensive sodium hydroxide, sodium carbonate, scrap iron, etc. to substitute low-value by-product of sodium sulfate into low-value by-product, sodium sulfate, or dangerous waste, residue, which are difficult to be reused. The material cost to be used as substitution amounts to more than 50% of the manufacture cost.
The current electrolysis reduction technology can effectively solve this problem: the reducing agent is added to produce a large quantity of residue and causes the secondary pollution during the pyrometallurgical process. It can also solve the pollution problem of producing a large quantity of high-temperature CO2, nitride gas and minim PbO, SO2, dioxin gas, etc., which cannot be avoided during the pyrometallurgical process. The electrolysis reduction technology has a higher recovery rate of metal lead and less pollution compared to the pyrometallurgical reduction process method. At present, there are mainly two types of common electrolysis reduction technology. It is described as follows:
(I) Solid Phase Electrolysis Reduction Process in a Wet Way
The main process flow is as follows: smashing and separating battery—coating plate manually with the diachylon consisting of PbSO4, PbO2 and PbO—solid phase electrolysis (NaOH electrolyte)—refining (in solid phase electrolysis, Na2SO4 is obtained)
There is no desulphurization process during the above-mentioned solid phase electrolysis reduction process. The separated diachylon after directly coating plate is electrolyzed in NaOH. During the electrolysis process, a large quantity of NaOH is consumed. NaOH produces Pb and Na2SO4 with PbSO4 in diachylon. As there are many kinds of metal oxide, such as PbSO4, PbO2, PbO, etc. in diachylon, Na2SO4 obtained during the electrolysis process electrolyte has a greater effect on the electrolyte. And electrolyte cycle system is not adopted to separate the electrolyte, causing unstable factors and higher power consumption.
(II) Electrolytic Deposition Process
The difference point to the above-mentioned solid phase electrolysis reduction process is that electrolysis deposition includes a desulphurization process. Its main flow is: smashing and separating battery—the diachylon consisting of PbSO4, PbO2 and PbO is desulphurized and converted with Na2CO3 or NaOH—thermal decomposition is used to disassociate PbO2 into PbO—silicofluoric acid is used to leach-out PbO as lead ion—deposition electrolysis reduction.
The desulphurization process in the electrolysis deposition process adopts the above-mentioned smashing pre-treatment substitution method of waste battery at a normal temperature.
Table 2 is a comparison table for the above two electrolysis processes
ProcessSolid phase electrolysis reductionElectrolysis deposition processtechnologyprocess in a wet wayin a wet wayProcessThere are no desulphurization and leadMaterial is sorted. Na2CO3 is used tocomparisondioxide disassociation processes afterconvert diachylon for desulphurizationraw material is sorted. Multi leadconversion. Thermal decomposition iscompounds are directly under solidused to disassociate PbO2 into PbO.phase electrolysis.Silicofluoric acid is used to leach out PbOas lead ion - deposition electrolysisreduction.DesulphurizationDuring the electrolysis process, NaOHSmashing pre-treatment method ofmethodis used to substitute sulfur in PbSO4.substitution at a normal temperature forwaste battery is adopted.DesulphurizationNaOH is used to substitute and removeNa2CO3 is used to substitute and removeschemesulfur during the electrolysis process, tosulfur. The cost is high. Na2SO4 treatmentcomparisonobtain Na2SO4. The treatment andand recovery is easier compared to therecovery are difficult. The cost (coolingsolid phase electrolysis reduction processelectrolyte) is very high. Lead(solid-liquid separation mode), but the costconsumption/T is larger than 150 Kgis very high. Lead consumption/T is largerNaOH.than 200 Kg Na2CO3.DeoxidationNo disassociation PbO2PbO2 is disassociated after substitution anddecompositionremoval of sulfur. One more process.PbO2 affectionPbO2 occupies more than 40% ofAlthough PbO2 is disassociated, the anodeon electrolysiselectrolysis material and poweris easy to regenerate PbO2 during theconsumption is 40% more.electrolysis process, which causes highpower consumption and unstable factor ofproduction.PbSO4 affectionElectrolysis process continuouslyPbSO4 is difficult to dissolve in theon electrolysisproduces Na2SO4 to cause elementsilicofluoric acid. The desulphurizationchange of the electrolyte and unstableconversion is thorough, which affectselectrolysis condition.direct metal recovery rate.Electrolysis24 hours, high power consumption,72~96 hours, high power consumption,cycle1000 KW/T sponge lead1400 KW/T electrolysis leadDe-lead mode ofSponge lead is formed. Na2SO4 isLead is sheet style, easy to fall off.pole plate andavailable, difficult to fall off.coating platemodeDirect recovery>85%>88%, non-thorough conversion part of(diachylon toPbSO4 and PbO2, unable to be electrolyzedsponge lead)and leached out.Product qualityLead purity >99.95%Lead purity >99.99%By-productNa2SO4 is less demanded on the market.Na2SO4 is less demanded on the market.The price is low. It is unable to be usedThe price is low. It is unable to be usedbattery manufacture in cycle.battery manufacture in cycle.ElectrolyteNaOH solutionSmell of silicofluoric acid is large.Production costHigh, electrolysis is uneven. OnlyTiptopsmall-scale production.
The electrolysis deposition process has been listed in Demonstration Catalogue for National Advanced Pollution Treatment Technology. Comparing with the current solid phase electrolysis reduction process, both processes have no waste to discharge out. They are favorable for environment protection, but there are still following shortcomings for the electrolysis deposition process in a wet way:                (1) Electrolysis cycle time is longer than that of the solid phase electrolysis reduction process and power consumption is higher.        (2) Desulphurization has to be very thorough. As lead sulfate is not dissolved in silicofluoric acid, desulphurization conversion rate is generally 97%. Therefore the cycle treatment quantity of leaching-out rate is increased.        (3) PbO2 existing makes electrolysis deposition very unstable. In diachylon, PbO2 occupies 40% of the contents. Although thermal decomposition method is adopted to decompose into PbO, a certain quantity of PbO2 is still not decomposed. During electrolysis process, it is easy to make ion produce PbO2 precipitation, which affects power consumption and stability of the electrolysis deposition process.        (4) Silicofluoric acid is used as electrolyte. The gas smell produced form silicofluoric acid is unpleasant.        (5) Cost is too high.        (6) There is still no way to implement full cycle regeneration of waste battery. It can only recover the diachylon from the waste battery in a form of meal lead to be recycled for producing lead acid battery. But the by-product Na2SO4 cannot be reused in battery manufacture.        